1. Field of the Invention
The present invention relates to an apparatus and method for dating a body or body sample, preferably, but not exclusively, a sample of a body fluid, such as blood, which is external to the body, for example, having caused stains on an external substrate, such as a floor, wall, and clothing.
2. Description of Related Art
It is well known that dating of external blood stains is a useful forensic technique to determine when a particular injury was caused to a person. Thus, the injury may have been such that the skin was punctured and blood was spilt. Alternatively, traces of other bodily fluids, such as saliva may be found. In both cases, however, there is a need to accurately determine the age of the stain or sample, so as to determine when the body fluid was released from the body.
In general, determination of the age of external blood stains has been carried out by a variety of methods. Although, historically, this was carried out by very roughly estimating the age based on the colour of the blood stain, more “scientific” methods have recently been employed. Most such methods rely on the fact that, when blood leaves the human body, haemoglobin in the blood is oxidised to met-haemoglobin. Various methods have therefore tried to use different characteristics of haemoglobin and met-haemoglobin to try to determine their relative concentrations and, from those, to try to determine the age of the blood stain. However, some of these methods require very complicated and advanced technical equipment, so that they cannot easily be done at the scene of the injury, for example a crime scene. In other cases, known techniques often compromise the blood traces by using chemicals or by requiring that the stains be taken to a laboratory in order to properly analyse them. Still others of the methods have proved not to be reliable since they provide too high a deviation compared to the actual age of the stains. One recent new technique that has been suggested is to use atomic force microscopy for high-resolution imaging of erythrocytes in a blood sample to detect elasticity changes on a nanometer scale (see the paper “Age determination of blood spots in forensic medicine by force spectroscopy” by Stefan Strasser, Albert Zink, Gerald Kada, Peter Hinterdorfer, Oliver Peschel, Wolfgang M. Heckl, Andreas G. Nerlich and Stefan Thalhammer published in Forensic Science International, Volume 170, Issue 1, 20 Jul. 2007, Pages 8-14).
In PCT Patent Application No. WO 2009/130580 there is described a technique for dating blood samples by taking a series of spectroscopic measurements of the sample to determine the concentrations of oxy-haemoglobin and met-haemoglobin at several spaced points in time. The ratios of the concentrations at the different points in time are then analysed to estimate when their concentrations were at a limit of their concentrations, thereby providing an indication of the age of the blood sample.
Although the above method is an improvement on the previous techniques, the estimate is based on the assumption that the reaction rate prior to the first measurement being made is the same (or at least roughly the same over the period) as the reaction rate over the time when the measurements are taken. Since it requires a series of measurements to be made, it can take some time for the estimate of the age of the sample to be determined. More accurate methods are therefore, of course, desirable.
Apart from body samples, it will be apparent that the assumption that the reaction rate prior to the first measurement being made is the same as the reaction rate when the measurements are taken also applies to other methods of dating of both body samples, and, in some cases, to methods of dating bodies, for example by taking the temperature of a body either once or several times and then assuming that it is cooling at a particular rate. However, such methods can be inaccurate because the cooling rate may depend on environmental factors.